A part of the hiccups in Android’s UI can certainly be traced to Java.
And explains why WP runs smoother on “old specs” hardware.
A significant chunk of Android runs in a VM as well. Framework, activity manager, window manager, system UI, etc… all have a lot of Java code and runs in dalvik, and the native parts are called via JNI.
Java kills the CPU’s caching mechanism by requiring that all objects be
referenced indirectly, risiding fragmented over the entire memory.
And while Java is a good high-level language, using it to implement low level
stuff that requires a lot of number or memory crunching is a bad idea. There are some forced design choices that make the language unsuitable for these tasks. A re-write of the OS to exclude this isn’t possible.
Leaves the only answer.
Hide the design choices of the past with more powerful CPUs & GPUs to provide enough brute force to overcome this.

Skins are another unnecessary burden layered on top of the OS.
It is well known these skins more laggy and buggy than the stock OS launcher.
Most now becoming very bloated and using up CPU cycles while adding to the increase risk of random crashes and the infamous forced closes running games.
Hope that helps steve